Most automotive vehicles with an air conditioning system have a condenser mounted in front of an engine cooling radiator. The two heat exchangers operate independently, but both are exposed to the same fan assisted cooling air stream pulled through the vehicle grill. The radiator works at much higher temperatures than the condenser, so the fact that the cooling air stream flows over the condenser first does not significantly affect the operation of the radiator. Conductive heat flow in the reverse direction, from radiator to condenser, would be highly detrimental, however, and has to be avoided. Since there is usually no direct structural interconnection between the two, direct heat conduction from radiator to condenser is generally not a problem.
The need for part reduction to shorten vehicle assembly time has led to the consolidation of vehicle components wherever possible. Because of their physical proximity and similarity in size and orientation, many attempts have been made, on paper at least, to integrate the condenser and radiator into a dual assembly that can be handled and installed as a unit. These attempts have failed to adequately take into account the realities of the manufacturing process, as well as structural and thermal performance in the vehicle. A brief review of the growing number of patents in this area shows designs the practical shortcomings of which are only now beginning to come to light.
Two early designs focused on one component, the corrugated cooling fins that are brazed between the adjacent pairs of parallel liquid tubes, and which are critical to transferring heat out of the fluid tubes and into the cooling air stream. In each design, the cooling fins represent the only significant common component between the radiator and condenser portions of the dual assembly. U.S. Pat. No. 5,000,257 discloses a dual assembly with two separate pairs of parallel tanks and two separate arrays of tubes extending between the tanks. The common structural connections between the two arrays of tubes consist first of a pair of reinforcing side plates, although no details of exactly how the reinforcements connect to the tanks are disclosed. Secondly, the corrugated cooling fins that serve the two arrays of tubes are common, extending across the central plane of the entire assembly. This arrangement is made possible by the fact that the tubes in the two arrays are equally spaced, and so arranged in coplanar pairs. The theory, apparently, was that while common side plates alone would have been enough to retain the condenser and radiator together as one unit, without the common cooling fins there would have been so little component commonality as to render the integration effort not worthwhile. The great drawback of common cooling fins serving both the radiator and condenser is that they represent a very effective, direct heat conduction path from one to the other, which severely effects thermal performance and efficiency. Consequently, a punched out, relieved area at the center of the cooling fin is provided to ostensibly reduce conductive cross flow. While such an approach would limit conductivity, it would not eliminate it, and would also make the fin much more difficult to manufacture.
Another similar design follows almost the same approach, but relies on the common corrugated cooling fins as literally the only structural interconnection between the radiator and condenser portions of the dual assembly. As seen in U.S. Pat. No. 5,033,540, the fins are also cut through almost completely at the center by a conduction reducing relief. However, this design could be impractical if not impossible to manufacture by conventional techniques. Heat exchangers typically lay flat on conveyer belts as they run through braze ovens, where they are heated to a very high temperature, a temperature high enough to melt and soften metal. This would especially effect metal cut down to a thin section. The central fin cut out shown in the '540 design is so severe that the upper half of the unit would almost surely sag down into the lower half in the oven. Secondly, even if the assembly could be properly supported in the braze oven, when it was installed in the vehicle, both portions of the unit would have to be securely and independently mounted onto the vehicle body. The common fins are so weakened at the center that they would not survive road vibration forces if only one portion of the dual assembly were secured to the vehicle body.
Another series of related and evolving designs, assigned to the assignee of the subject invention, are structurally robust and simple from a manufacturing standpoint, and have a high degree of structural unitization. But they have not been optimized in terms of thermal performance. U.S. Pat. No. 5,009,262, the earliest design, had a very high degree of structural commonality. In fact, essentially every paired component and part that could be integrated into one part was so combined, including combining the four tanks into a one pair of bifurcated, extruded tank units, with a central, integral dividing wall. Tubes and fins were also combined. Unfortunately, this also provided a maximum amount of direct heat conductive path between the radiator and condenser portions of the dual assembly, especially through the common tank divider walls and common fins. Later evolutions of the design attempted to reduce the conductive heat flow without really departing from the basic design. In U.S. Pat. No. 5,163,507, an enclosed conduction reducing slot was coextruded in the tank dividing wall. In U.S. Pat. No. 5,186,243, an open, slightly more effective conduction reducing slot is shown in the tank divider wall. In U.S. Pat. No. 5,186,244, the common tubes are thinned in the middle and notched, using an approach similar to what was done to the tank wall in the '243 patent. In U.S. Pat. No. 5,186,246, the tank is not a completely integral extrusion, but instead has a separate stamped and slotted header plate, which is crimped down onto a central dividing wall of an open extrusion to enclose it. A tank with a separate header plate is much more manufacturable than a completely integral extrusion. The design shown has just as much direct conductive flow path between the two halves of the tank as the integral extruded tank, however.
In conclusion, there is still a need for a dual condenser and radiator assembly in which the constituent components are relatively simple to manufacture and assemble, and at least commonized, if not integrated, and in which the interconnection between the condenser and radiator portions of the assembly is structurally sufficient, but not so great as to significantly impair thermal performance.